Microbial quality and persistence of enteric pathogens in graywater from various household sources

This study was designed to evaluate the microbial quality and safety of graywater for reuse purposes. The microbial and chemical composition of graywater from shower/bath, wash cycle and rinse cycle of a clothes washing machine was determined. Graywater composed from all sources within a house was also monitored each week over a 2-3-month time period. Samples were taken from a diverse group of families with children (18 months-9 years of age) and without children. Standard plate count bacteria (SPC) ranged from 10⁵ to 10¹⁰ colony forming units (cfu) per 100 ml for shower and bath water, and an average of 10⁴ to 10⁶ cfu per 100 ml for total coliforms. Families with small children produced wash cycle graywater containing 10⁶ cfu per 100 ml of fecal coliforms. During investigations on storage of graywater, it was found that total bacterial SPC and coliform baceria increased one order of magnitude. Salmonella atyphimurium and Shigella dysenteriae seeded into graywater were found to persist for at least several days. Poliovirus type 1 added to graywater decreased 99 and 90% at 25 and 17°C, respectively, after 6 d of storage in graywater. These data imply that there may be some risk associated with reuse of graywater when these pathogenic bacteria or viruses are being excreted by an individual producing the graywater.